We performed micro-X-ray fluorescence imaging of frozen-hydrated sections of a root of Pteris vittata for the first time, to the best of our knowledge, to reveal the mechanism of arsenic (As) uptake. The As distribution was successfully visualized in cross sections of different parts of the root, which showed that (i) the major pathway of As uptake changes from symplastic to apoplastic transport in the direction of root growth, and (ii) As and K have different mobilities around the stele before xylem loading, despite their similar distributions outside the stele in the cross sections. These data can reasonably explain As reduction, axially observed around the root tip in the direction of root growth and radially observed in the endodermis in the cross sections, as a consequence of the incorporation of As into the cells or symplast of the root. In addition, previous observations of As species in the midrib can be reconciled by ascribing a reduction capacity to the root cells, which implies that As reduction mechanisms at the cellular level may be an important control on the peculiar root-to-shoot transport of As in P. vittata.

中文翻译：

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凤尾根冷冻水合切片中砷的同步加速X射线荧光成像。

据我们所知，我们首次对凤尾蕨根的冷冻水合切片进行了X射线荧光成像，以揭示砷（As）吸收的机理。在根的不同部分的横截面中成功地观察到了As的分布，这表明（i）As吸收的主要途径在根的生长方向上从共生向质外传递转变，并且（ii）As和K具有不同的变化尽管木质部在横截面中的分布相似，但在木质部加载之前，石碑周围的迁移率是相似的。这些数据可以合理地解释As的减少，这是由于As掺入到根的细胞或共生体中的结果，沿根部生长方向在根尖周围沿轴向观察到，在横截面的内胚层中沿径向观察到。